Initial Configuration

The neutron star obeys a polytropic equation of state, P = Kρ₀ ^Γ, at t = 0. It is evolved according to the adiabatic evolution law, P = (Γ-1)ρ₀ε, where P is the pressure, K is the polytropic gas constant, ε is the internal specific energy, Γ is the adiabatic index, and ρ₀ the rest-mass density. We chose Γ = 2 to mimic stiff nuclear matter. This star is irrotational (nonspinning) and in a quasiequilibrium circular orbit.

Black Hole

For the spinning BH we consider the mass ratio q = M_BH/M_NS = 3. It is spinning rapidly, with S_BH/M_BH² = 0.75.

Neutron Star

The initial compaction of the neutron star is M_NS/R_NS = 0.145. The rest mass is 83% of the maximum rest mass of an isolated, nonrotating NS with the same polytropic EOS. It has a radius of R_NS = 13.2 km (M₀/1.4 M_ʘ) and a mass of M_NS = 1.30 M_ʘ (M₀/1.4 M_ʘ). In the cases where the neutron star has a magnetic field, B_max ~ 10   ¹⁷G and ⟨ B ²/8πP ⟩ = 0.005.

Binary

The initial binary is in a quasiequilibrium circular orbit, and has a frequency of MΩ = 0.032. The initial coordinate separation is D/M = 8.80. The matter and gravitational field variables are determined by using the conformal thin-sandwich formalism. BH equilibrium boundary conditions are imposed on the BH horizon.

The metric (gravitational field) is determined by integrating the Einstein field equations according to the BSSN prescription. The matter and electromagnetic fields are evolved by solving the equations of relativistic hydrodynamics via a high-resolution, shock-capturing (HRSC) scheme.

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